1. Field of the Invention
The present invention relates to a commutator for use with a DC motor or a DC generator and, more particularly, to an improvement in the construction of commutator segments (which will be hereafter referred to as "segments"), which is effective when applied to a commutator having its segments on their parent metal surfaces covered with protecting portions.
2. Related Art Statement
In some commutators for coping with gasohol, the segments have their parent metal of copper cladded with protecting portions of a silver-nickel alloy on at least its surface for contacting brushes (as is disclosed in Japanese Utility Model Laid-Open No. 60-135063, for example).
A process for manufacturing such commutators includes: the step of curling a material plate of copper covered with a cladding plate into a cylindrical shape; the step of forming a boss of a resin in the hollow portion of the cylinder by fitting the cylinder in a molding die; and the step of longitudinally slitting the cylindrical material plate and the cladding plate to form a plurality of segments.
In this commutator manufacturing process, since there is difference in level between the outer circumference of the copper plate and the cladding plate, the step of molding the boss of a resin in the cylinder is accompanied by problems that the material plate is deformed by the resin injection pressure and that the resin flows out of the cylinder.
On the other hand, some commutators to be used with a DC motor or the like are so constructed that a group of segments are anchored at the outer circumference of the boss molded of an insulating material.
A process for manufacturing such commutators is effected: by cutting one end portion of a cylinder of a conducting material to arrange a plurality of notches circumferential equi-distantly thereby to form riser members; by subsequently setting the cylinder in a molding die while positioning the riser members in respective holes formed in advance in the die; by injecting an insulating material into the hollow portion of the cylinder to form a boss; and by subsequently cutting the trunk of the cylinder to arrange each of a plurality of slits between adjacent two of the riser members thereby to form the individual segments.
The processes described above for manufacturing those commutators are accompanied by the following problems because the riser members are fitted in the respective holes of the molding die:
(1) The workability is low;
(2) The resin is liable to remain in each of the holes of the molding die thereby to make insertions of the riser members insufficient; and
(3) In the case of using a cylinder cladded with a protecting material (as in a later-described embodiment 2), the parent metal of the cylinder is annealed to make the riser members liable to be bent thereby to cause the insufficient insertions.